The present invention relates to industrial control systems and in particular to an interface communicating with data networks normally used in industrial control systems.
Industrial controllers are special purpose computers used for controlling industrial processes or manufacturing equipment. Under the direction of a stored program, the industrial controller examines a series of inputs reflecting the status of the controlled process and changes outputs affecting the control of the process. The inputs and outputs are most simply binary, that is xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d, however analog inputs and outputs taking on a continuous range of values are also used. The binary inputs and outputs may be represented by single bits of data, the analog inputs and outputs may be represented by multiple bit data words.
The various components of an industrial controller are often spatially distributed about a factory or manufacturing facility to be interconnected by one or more communication networks. These communication networks are characterized by being highly reliable and by delivering data with a minimal and well defined delay, as is required for real-time control. A number of different communication networks are commonly used in the industrial controller art including but not limited to: ControlNet; DeviceNet and EtherNet whose specifications are published and whose protocols are used broadly by a number of manufacturers and suppliers. These communication networks differ from one another in physical aspects, for example, the type of media (e.g., co-axial cable, twisted pair light fiber, etc.); the protocols of its operation, (e.g., Baud rate, number of channels, word transmission size, use of connected messaging, etc.) and how the data is formatted and how it is collected into standard messages.
A common component of the industrial controller is an input or output (I/O) module which accepts data for a central control computer from the controlled process or machine, and provides data from the central control computer to the controlled process or machine. I/O modules are typically remote from the central control computer and connected via a communications network as described above.
With the increasing processing power of general purpose xe2x80x9cdesktopxe2x80x9d computers, and in particular those based on microprocessors manufactured by the Intel Corporation, special purpose control computers may no longer be required for low-end control applications. xe2x80x9cSoft PLCxe2x80x9d (programmable logic controller) programs exist that allow a high-end desktop computer, often with multiple processors, to simulate the operation of a special purpose central control computer. Such soft PLC programs execute programs written in, for example, relay-ladder language to control plug-in I/O modules communicating control signals between the desktop computer and the controlled process.
The large installed base of desktop computers has resulted in powerful and inexpensive computer languages, development systems, desktop operating systems, principally the Windows NT graphical operating system manufactured by Microsoft Corporation. Ideally these languages and tools could be used to directly program a desktop computer to work with standard industrial controller communication networks and I/O modules without the need for a specialized Soft PLC type shell. Unfortunately the task of writing interfaces to standard industrial control networks, which have complex protocols required for the reliable and timely transmission of data, makes direct programming a desktop computer as an industrial controller, cumbersome. A programmer wishing to write a control program using a standard language, such as C, must become an expert with a number of intricate timing and protocol issues associated with the various industrial control networks.
The present invention provides a circuit card that may be attached to a desktop computer to allow a simple programming interface to a wide variety of industrial controller communication networks. A processor on the circuit card executes a run-time program and communicates data between application programs and the communication networks, using the convention of a standard xe2x80x9capplication programmer""s interfacexe2x80x9d (API) normally provided by the operating system to allow control of standard computer hardware such as disk drives and video monitors. Special extension API functions are provided for reading and writing to a communication network and for collecting data from various devices on the network into a logical unit called a xe2x80x9cviewxe2x80x9d. The details of the communication networks and their protocols are made invisible to the programmer.
Specifically then, the present invention provides a multi-network interface connecting a computer with a plurality of industrial control, communication networks employing different protocols to exchange data with remote I/O devices, where the computer executes at least one application program and an operating system and wherein the operating system provides an application programmer""s interface allowing the application program to communicate with the computer hardware.
The multi-network interface includes network connections communicating with at least one industrial control network, a configuration database storing information indicating the communication protocol of any connected industrial control network and an API extension integrated with the API of the operating system defining functions for communication on the different networks. A processor communicating with the network connection, the computer, and executing a run-time program communicates data between the application program and the network connection to the API extensions according to the protocols indicated in the configuration database.
Thus it is one object of the invention to provide for a uniform and simple interface between application programs and industrial control networks regardless of the protocols of the latter. By making use of the API, the power of commercially available desktop development environments may be tapped and the need for proprietary development systems or specialized software environments is avoided.
It is another object of the invention to allow for upgrading and changing of network protocols for industrial controller networks without requiring rewriting of industrial controller software. Changes in network protocol require only a change in the network controller and possibly just in the configuration database of the network controller.
The multi-network interface may further include an attribute file associating a unique handle with at least one device on at least one network and the processor may further execute the run-time program to communicate predefined collections of data between the application program and the devices according to a handle provided in an API call.
Thus, it is another object of the invention to allow arbitrary groupings of devices on an industrial control network to be collected for the purpose of exchanging data between the devices and an application program. By placing a definition of this grouping in an attribute file of the multi-network interface, the application programmer""s task is much simplified. For example, data on multiple networks may be manipulated as if on a single network.
The API extensions include at one API extension allowing the application program to define a handle and its associated devices.
Thus, it is another object of the invention to allow the application programmer to collect devices as a logical entity within the application program for data communication regardless of the particular networks or devices on the network.
The processor may execute the run-time program to reset watchdog timers on the networks according to protocols indicated in the configuration database.
Thus it is another object of the invention to allow desktop type computers to co-exist with high reliability networks used in industrial control where it is critical to monitor the network health and the health of the controlling processor. By allowing the interface to handle watchdog timers, reliable monitoring of the network and controlling computer may be allowed.
The attribute file may further include an ownership attribute associated with only one handle and the processor may execute the run-time program to allow writing of data to a device on a network only if the handle associated with the API extension indicates ownership of the device. Thus is yet another object of the invention to provide for a highly reliable multi-tasking environment on a desktop type computer by preventing the possibility of two tasks writing conflicting data to an I/O point in the controlled process such as may produce unpredictable behavior in a control environment. By establishing within the multi-network interface, single ownership of each device on a network, such conflicts may be prevented.